Commit 7acf8a1e authored by Matthew Whitehead's avatar Matthew Whitehead Committed by David S. Miller
Browse files

Replace 2 jiffies with sysctl netdev_budget_usecs to enable softirq tuning 



Constants used for tuning are generally a bad idea, especially as hardware
changes over time. Replace the constant 2 jiffies with sysctl variable
netdev_budget_usecs to enable sysadmins to tune the softirq processing.
Also document the variable.

For example, a very fast machine might tune this to 1000 microseconds,
while my regression testing 486DX-25 needs it to be 4000 microseconds on
a nearly idle network to prevent time_squeeze from being incremented.

Version 2: changed jiffies to microseconds for predictable units.

Signed-off-by: default avatarMatthew Whitehead <tedheadster@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 20da848f

Documentation/sysctl/net.txt

+10 −1
Original line number Diff line number Diff line
@@ -188,7 +188,16 @@ netdev_budget 


Maximum number of packets taken from all interfaces in one polling cycle (NAPI

poll). In one polling cycle interfaces which are registered to polling are

probed in a round-robin manner.

probed in a round-robin manner. Also, a polling cycle may not exceed

netdev_budget_usecs microseconds, even if netdev_budget has not been

exhausted.



netdev_budget_usecs

---------------------



Maximum number of microseconds in one NAPI polling cycle. Polling

will exit when either netdev_budget_usecs have elapsed during the

poll cycle or the number of packets processed reaches netdev_budget.



netdev_max_backlog

------------------

include/linux/netdevice.h

+1 −0
Original line number Diff line number Diff line
@@ -3296,6 +3296,7 @@ static __always_inline int ____dev_forward_skb(struct net_device *dev, 
void dev_queue_xmit_nit(struct sk_buff *skb, struct net_device *dev);



extern int		netdev_budget;

extern unsigned int	netdev_budget_usecs;



/* Called by rtnetlink.c:rtnl_unlock() */

void netdev_run_todo(void);

include/uapi/linux/sysctl.h

+1 −0
Original line number Diff line number Diff line
@@ -274,6 +274,7 @@ enum 
	NET_CORE_AEVENT_ETIME=20,

	NET_CORE_AEVENT_RSEQTH=21,

	NET_CORE_WARNINGS=22,

	NET_CORE_BUDGET_USECS=23,

};



/* /proc/sys/net/ethernet */

kernel/sysctl_binary.c

+1 −0
Original line number Diff line number Diff line
@@ -197,6 +197,7 @@ static const struct bin_table bin_net_core_table[] = { 
	{ CTL_INT,	NET_CORE_AEVENT_ETIME,	"xfrm_aevent_etime" },

	{ CTL_INT,	NET_CORE_AEVENT_RSEQTH,	"xfrm_aevent_rseqth" },

	{ CTL_INT,	NET_CORE_WARNINGS,	"warnings" },

	{ CTL_INT,	NET_CORE_BUDGET_USECS,	"netdev_budget_usecs" },

	{},

};

net/core/dev.c

+3 −1
Original line number Diff line number Diff line
@@ -3441,6 +3441,7 @@ EXPORT_SYMBOL(netdev_max_backlog); 


int netdev_tstamp_prequeue __read_mostly = 1;

int netdev_budget __read_mostly = 300;

unsigned int __read_mostly netdev_budget_usecs = 2000;

int weight_p __read_mostly = 64;           /* old backlog weight */

int dev_weight_rx_bias __read_mostly = 1;  /* bias for backlog weight */

int dev_weight_tx_bias __read_mostly = 1;  /* bias for output_queue quota */
@@ -5307,7 +5308,8 @@ out_unlock: 
static __latent_entropy void net_rx_action(struct softirq_action *h)

{

	struct softnet_data *sd = this_cpu_ptr(&softnet_data);

	unsigned long time_limit = jiffies + 2;

	unsigned long time_limit = jiffies +

		usecs_to_jiffies(netdev_budget_usecs);

	int budget = netdev_budget;

	LIST_HEAD(list);

	LIST_HEAD(repoll);

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